Creation of Gas-Phase Organo-Uranium Species by Removal of "yl" Oxo Ligands From UO Carboxylate Precursor Ions.

Rationale: These experiments were conducted to measure the diversity of organo-U (IV) and U (III) ions created using multiple-stage tandem MS and collision-induced dissociation of halogen-substituted UO-phenide complexes [UO(CHFX)], X = Cl, Br, or I.

Methods: Samples of UO(OC-CHFX) were prepared by digesting UO with appropriate halogen-substituted carboxylic acids in deionized water. Solutions for ESI were created by diluting the digested sample in 50:50 HO/CHOH. Precursor ions for multiple-stage tandem MS were generated by electrospray ionization (ESI). Multiple-stage collision-induced dissociation (He collision gas) in a linear quadrupole ion trap mass spectrometer was used to prepare species such as [UFX(C≡CH)] and UF(C≡CH)] for subsequent study of ion-molecule reactions with adventitious neutrals in the ion trap.

Results: Multiple-stage CID of the [UO(CHFX)], X = Cl, Br, or I, complexes caused removal of both "yl" oxo ligands from of the UO moiety to create ions such as [UFX(C≡CH)] and [UFX]. For [UFXC≡CH] and [UFC≡CH] products, hydrolysis to generate [UFX (OH)] and [UF (OH)], with concomitant loss of HC≡CH, was observed. CID of [UO(CHFBr)] and [UO(CHFI)] caused reductive elimination of the respective halogen radicals to generate interesting organo-U (III) species such as [UF(C≡CH)] and [UC].

Conclusions: The use of "preparative" tandem mass spectrometry and a suite of halogen substituted benzoic acid ligands can be used to remove both oxo ligands of UO and generate a group of homologous organo-U (IV) and organo-U (III) ions for studies of intrinsic reactivity.